Spectacles are a structure usually worn in front of the eyes, comprising at least one spectacle lens serving to protect the eye or to correct defective vision and positional errors of the eyes. Spectacle lenses for correcting defective vision are therefore also referred to as corrective lenses or optically effective spectacle lenses. By way of example, such spectacle lenses could be single vision lenses on multi-focal lenses, in particular bifocal lenses, trifocal lenses or else varifocal lenses. By way of example, defective vision could include shortsightedness (myopia), farsightedness (hyperopia), astigmatism and further states of vision which deviate from the norm and/or are suboptimal. The defective vision also includes age-related farsightedness (presbyopia).
Corrective lenses are distinguished as positive lenses and negative lenses. A positive lens has a converging optical effect that magnifies the observed object. A negative lens has a diverging optical effect that reduces the observed object.
Spectacle lenses are usually produced specifically to order according to the specific demands adapted to the individual spectacle wearer. In general, the spectacle lenses are manufactured by using a restricted number of different types of semifinished spectacle lens blanks, the so-called semifinished products, which are stored by the spectacle lens manufacturer. Spectacle lens semifinished products, just like spectacle lens finished products, each have an optical surface destined for the object side and an optical surface destined for the opposite eye side arrangement for the spectacle wearer; and a surface spacing these apart. The optical surface destined for arrangement on the object side is referred to as front surface; the optical surface destined for arrangement on the eye side is referred to as back surface. The surface lying therebetween, which either directly forms an edge or indirectly adjoins the front surface at one end and the back surface at the other end by way of an edge surface, is referred to as cylinder edge surface. In general, the front surface has a convex curvature; the rear surface is concave.
What form must be obtained by the spectacle lens in order to obtain the desired optical correction is decisively determined by the material thereof. Here, the most important parameter is the refractive index of the material. While spectacle lenses were predominantly produced from mineral glasses in the past, in particular crown glasses (Abbe number>55) and flint glasses (Abbe number<50), spectacle lenses from a multiplicity of organic materials have become available in the meantime. Such base materials for organic spectacle lenses are offered under the trade names CR 39, MR 8, MR 7, CR 330 and MR 174. A selection of such base materials is also found in the published specification EP2692941 A1. Other materials are continuously being tested and developed in respect of the suitability thereof for organic spectacle lenses. Table 1, below, elucidates characteristic variables and reference variables of a selection of known base materials:
Average refractiveAbbeTrade nameBase materialindex nenumber veCR 39Poly allyl diglycol1.50056CR607carbonateCR630TrivexPolyurea/Polyurethane1.53045PCPolycarbonate1.59029MR 8Polythiourethane1.59841MR 7Polythiourethane1.66432MR 10Polythiourethane1.66632MR 174Poly(episulfide)1.73832Mineral 1.51.52558Mineral 1.61.60444
Currently, a large number of organic spectacle lens semifinished products or finished products with spherical, rotationally symmetric aspherical or progressive front surfaces are cast in mass production in prototypes with front and back surface form shells, which are spaced apart from one another by means of a sealing ring, forming a cavity in the process, as described in, for example, the documents U.S. Pat. Nos. 4,300,821, 6,103,148A or JP2008191186 A. This applies to base materials with the trade names MR 7, MR 8, MR 10 and CR 39, CR 607, CR 630, et al. The base materials with the trade names MR 7, MR 8, and MR 10 are polythiourethanes marketed by Mitsui Chemicals. Here, the abbreviation “MR” stands for Mitsui Resin. CR 39 or Columbia Resin 39 is the brand name selected by Pittsburgh Plate Glass Industries (PPG Industries) under which the material poly diethylene glycol bis allyl carbonate or poly allyl diglycol carbonate (abbreviation: PADC) is marketed. This is a highly-refractive duroplastic polymer material. CR 607 and CR 630 are also produced by PPG. The materials CR 607 and CR 630 are used for example for photochromic applications.
Semifinished products of finished products for spectacle lenses made out of polycarbonate are generally produced in metal forms by means of an injection molding technique. This production method is described in, for example, EP 0955147 A1.
Mineral spectacle lenses are generally produced by machine-based mechanically abrasive machining of a blank.
The semifinished products or finished products described above are often subjected to one or more finishing processes. In particular, functional layers are applied to one or both sides. Such functional layers are layers which equip the spectacle lenses with predetermined properties, which are advantageous to the spectacle wearer and which the spectacle lenses would not have purely on the basis of the property of the basic or carrier material, onto which the functional layers are applied where necessary, and the forming. In addition to optical properties, such as an antireflection coating, silvering, light polarization, coloring, self-tinting et cetera, such advantageous properties also include mechanical properties, such as hardening, reduction of the adherence of dirt or reduction in steaming up, et cetera, and/or electrical properties such as shielding from electromagnetic radiation, conductance of electrical current, et cetera, and/or other physical or chemical properties.
Order-specific prescription spectacle lenses, that is, in particular, individualized single vision and multi-focal lenses, the optical properties of which are not standardized in a preselectable manner, at least in part, but which are individually calculated and manufactured in a manner adapted to the user in relation to the dimensions and/or the arrangement thereof on the spectacle lens, and, in particular, varifocal or progressive lenses are brought into their final form by mechanical, in particular deforming and/or abrasive, methods. Here, the outer forms may have a round, oval or arbitrary embodiment, describing a so-called free form in the latter case.
One surface of the semifinished spectacle lens blank forms the final surface of the finished spectacle lens. The other surface is machined in such a way that the optical system of the finished spectacle lens corresponds to the ophthalmic prescription of the spectacle wearer. In general, provision is made for the front surface to form the final front surface of the finished spectacle lens. Relatively small machining of the final front surface may be undertaken, but always without the curvature thereof being modified. In particular, it is possible for one or more functional layers of the type described above to be applied. Accordingly, spectacle lens semifinished products are lens blanks with only one surface where machining in optical terms has been completed (cf. Heinz Diepes, Rolf Blendowske “Optik and Technik der Brille”, Optische Fachveröffentlichung GmbH, Heidelberg, 2002, page 560). As will be once again clarified below, the present invention only relates to the spectacle lens semifinished products with a spherical or rotationally symmetric aspherical front surface and a back surface to be machined in accordance with the ophthalmic prescription of the spectacle wearer.
Within the scope of the present invention, and pursuant to section 11.3 of the DIN standard EN ISO 13666:2012 (ophthalmic optics—spectacle lenses vocabulary) incorporated herein by reference, the nominal surface power value or the nominal curvature of the front surface of a spectacle lens is referred to as base curve. Alternatively, the term basic curve is also used instead of a term base curve. The refractive index assumed during the measurement should be specified if the nominal surface power value is specified. If flagged appropriately, it would also be possible to specify the nominal curvature or the nominal radius of curvature instead of the surface power value. Even though DIN EN ISO 13666:2012 only refers to the front surface of a single vision lens in view of the designation as base curve, below a base curve refers, in general, to the nominal surface power value at the center of a rotationally symmetric front surface of a spectacle lens semifinished product which is suitable not only for the production of single vision lenses but also for the production of multi-focus lenses. In the case of the rotationally symmetric aspherical surfaces, the nominal curvature corresponds to the vertex curvature. In the case of the rotationally symmetric aspherical surfaces, the nominal radius of curvature corresponds to the vertex radius.
In general, the base curves are specified with reference to a standard refractive index of 1.53. However, other refractive indices may also be used in order to specify base curves.
Typically, the spectacle lens manufacturers produce a series of semifinished spectacle lens blanks, which each have a dedicated base curve. This “base curve series” is a set of semifinished products, the nominal front face curvatures and power values increase in steps (for example, +0.50 D, +2.00 D, +4.00 D and so on), as described in, for example, Shamir: “Shamir Quick Reference Guide”, Dec. 6, 2013, pages 1 to 5; retrieved on 9/16/2015 from the Internet; URL: http://www.shamiroptic.de/images/shamir.pdf.
The nominal surface power value or the nominal curvature is used for labeling purposes and also referred to as nominal basic curve. The actual surface power value or the actual curvature is used for the calculation. It is also referred to as actual basic curve. In the following explanations, reference is made to the actual values, that is, the actually present surface power value, the actually present curvature and the actually present radius of curvature of the surfaces—taking into account the usual manufacturing and measurement tolerances—unless reference is explicitly made to the nominal values.
The front face of a semifinished product of a base curve series serves as a starting point to calculate the optical surface of the back surface and according to which the final spectacle lens according to the prescription of a spectacle wearer is produced.
The front faces of the semifinished lens blanks of a base curve series may, in principle, be both rotationally symmetric surfaces, such as, for example, spheres or rotationally symmetric aspherical surfaces, and non-rotationally symmetric surfaces, such as, for example, toric surfaces or else varifocal surfaces. The latter may also be embodied without any symmetry property. In this case, they are referred to as free-form surfaces. Only spectacle lens semifinished products with rotationally symmetric, that is, spherical or rotationally symmetric aspherical, front surfaces are relevant within the scope of the present invention.
By way of example, after selecting a semifinished lens blank from a set of semifinished products with different spherical or rotationally symmetric aspherical front faces, progressive addition lenses (PALs) may be produced by pure machine-based machining of the back surface taking into account the individually required addition, the prescription values and, optionally, further individual requirements of the spectacle wearer, as is described in, for example, U.S. Pat. No. 6,089,713, WO2004/019243 A1 or U.S. Pat. No. 8,313,194. The back surface does not have point symmetry and/or axial symmetry, but has multifocal properties.
Each base curve in a series is usually used for the production of a plurality of prescriptions, which are recommended by the manufacturer of the semifinished product set. The manufacturers provide so-called base-curve selection charts, from which the different prescriptions, for which the use of the respective base curve in the series is recommended, can be gathered.
An example of a typical base-curve selection chart can be gathered from the patent document U.S. Pat. No. 6,948,816. The base curve series shown in FIGS. 23A to C of this patent document consists of five base curves. The selection chart shows the base curve recommended by the manufacturer in accordance with a given prescription as a function of the spherical effect and the cylindrical effect for correcting an astigmatic aberration. The shown selection chart relates to progressive lenses (PALs), in which the optical effect changes between distance part and near part. In general, the same type of selection chart is used for every type of spectacle lens, such as, for example, (spherical and/or toric) single vision lenses, bifocal lenses, aspherical lenses and PALs.
Two further examples of base-curve selection charts are gathered from FIGS. 2 and 3 in EP2028527 B1. The base curve series according to FIG. 2 consists of eight base curves, which are labeled by the numbers “1” to “8” and the base curve series according to FIG. 3 comprises fourteen base curves, which are labeled by the numbers “1” to “14”. The nominal refractive power of the fourteen spherical base curves of the base curve series according to FIG. 3 increases in the following steps: 0.75; 1.00; 1.50; 2.00; 2.75; 3.25; 3.75; 4.25; 5.25; 5.75; 6.25; 6.50; 7.50; 8.50 from 0.75 D to 8.50 D.
From U.S. Pat. No. 8,313,194, it is possible to gather that the general trend consists of restricting the number of different base curves of a base curve series in order to minimize the number of molds, the costs for storage and the requirements placed on storage. Therefore, a standard base curve series comprises at most twenty base curves (cf. EP2028527 B1: paragraph [0013]), such as, for example, ten (cf. EP0857993 A2: page 5, lines 38-51) or five base curves (U.S. Pat. No. 6,948,816: FIGS. 23A to C).
The documents specified in the two paragraphs above all consider the subject of optimizing the base curves of a base curve series for spectacle lenses made of a predetermined base material. Presumably, the authors of these documents assume manufacturing at the large spectacle lens manufacturers.
From WO2004/019243 A1 set forth at the outset, it is possible to gather that it is desirable for, in particular, the individual varifocal spectacle lenses described above to be able to be produced not only by a few spectacle lens manufacturers, but also locally in wholesale businesses, large laboratories and the like, as are currently active in many markets.